A water body characterized by nutrient rich water supports abundant growth of phytoplanktons and other water plants on its surface. Over time, the water body gets filled with a large number of such plants and the process is called Eutrophication. In such water bodies, dissolved oxygen content is nil or very less.
In eutrophicated water body, growth rate of phytoplankton is high because of:

Options

A. Light penetrating the lower surfaces of water body
B. Enrichment of nutrients in the water body
C. Less of dissolved oxygen in the water body.
D. Aquatic fauna flourishes well in eutrophicated water body

Explanation

**Step-by-Step Solution:**

1. **Understanding Eutrophication**: Eutrophication is a process that occurs in water bodies when there is an excess of nutrients, particularly nitrogen and phosphorus. This leads to an overgrowth of aquatic plants and phytoplankton.

2. **Role of Nutrients**: The primary reason for the high growth rate of phytoplankton in eutrophicated water bodies is the enrichment of nutrients. These nutrients are essential for the growth and reproduction of phytoplankton, which are single-celled microalgae that perform photosynthesis.

3. **Photosynthesis and Oxygen**: Phytoplankton can produce their own food through photosynthesis, which also allows them to generate oxygen. They do not rely heavily on the dissolved oxygen in the water, as they can obtain oxygen from the atmosphere due to their presence at the water's surface.

4. **Evaluating the Options**:
- **Option A**: Light penetrating the lower surface of water bodies is not a significant factor because phytoplankton live at the surface where light is abundant.
- **Option B**: The enrichment of nutrients is the main reason for the high growth rate of phytoplankton in eutrophicated water bodies.
- **Option C**: Less dissolved oxygen does not hinder phytoplankton growth since they can photosynthesize and access atmospheric oxygen.
- **Option D**: Aquatic fauna struggles in eutrophicated waters due to low oxygen levels, which does not contribute to phytoplankton growth.

5. **Conclusion**: The correct answer is that the growth rate of phytoplankton is high in eutrophicated water bodies primarily due to the enrichment of nutrients.

**Final Answer**: B. Enrichment of nutrients in the water body.

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